Method of and apparatus for forming metal strips



Feb. 18, 1964 G. J. sowls'rocK 3,121,631

METHOD OF AND APPARATQS FOR FORMING METAL STRIPS Filed Sept. 11, 196144%, C094 w T T awE-ys United States Patent 3,121,631 METHOD ()F ANDAPPARATUS FOR FORMING METAL STRIPS Gregory J. Comstock, Essex, Conn.,.assiguor to Ehe Comstoelr Company, Hi ganum, Colin a corporation ofConnecticut Filed Sept. 11, 1961, Ser. No. 137,219 6 Qlaims. (Cl.75-214) This invention relates to the art of either high density orporous metal sheet or web formation and contemplates the provision of animproved metal product, and to a novel method of, and an apparatus for,fabricating the same. More particularly defined the invention isconcerned with the art of powder metallurgy and provides an improvedmethod of, and apparatus for, converting a metal or alloy powder, or amixture of metal or alloy powders with or without nonmetallic powdersinto a solid metallic product having the desired dimensions and havinguniform physical characteristics throughout. Advantageously the improvedmethod and apparatus may be employed in the continuous fabrication ofstrips or webs of powdered metal which strips may be subsequentlyfashioned into commercially useful strips or sheets by other procedures,as by rolling, heat treating, etc.

It has heretofore been proposed that elongated metal shapes may beformed from metal powders by feeding dry metal powders from a bin or thelike into and through the pass between closely spaced paralleloppositely rotating rolls so as to form the metal powder into strips,such strips of powdered metal then being sintered, rolled and thenannealed to produce the finished product.

It has been found, however, that strips of powdered metal which areformed in the manner described are generally nonuniform in texture andcharacter, having certain areas in which the metal is more closely ordensely compacted than it is in other areas, thus promoting or bringingabout nonuniformity in the finished product. It has been suggested that,by adding suitable lubricating agents to the dry powdered metal thisdifliculty may to some extent be overcome, but it has been generallyfound that, even in those processes in which lubricant is employed, thestrip of powdered metal is not in best condition for subsequent workingor use because of nonuniformity of distribution of the powder of whichthe strip is composed. It has also been found that when a mixture ofpowdered metal and a lubricant is placed in a mold and compressedcertain portions of the resulting article will unavoidably have beencompacted to a greater extent than other portions.

We have discovered that such undesirable variations of density inarticles formed from a metal or alloy powder, or mixtures of metalpowders, may be avoided by utilizing a liquid of such character orconsistency that it will support individual particles of metal powderintroduced into the liquid equidistantly from each other, or uniformlydispersed throughout the bath, and thereafter casting, extruding,flowing or otherwise delivering the metal carry liquid, or slip in suchmanner as to form a strip or sheet upon a carrier or support. The sheetor strip of metal powder carrying liquid thus deposited is of uniformcharacter throughout and, after drying, and preferably after the driedstrip has been remoistened, may be further processed with mostsatisfactory results. The liquid employed as a suspending medium for thepowder supports the powder in such manner as to form with it a colloidalsuspension.

The improved method contemplates the initial formation of a bathcomprising metal powder suspended in a liquid vehicle such as an aqueoussuspension of sodium or ammonium alignate or of liquid methanol or other3,121,631 Patented Feb. 18, 1964 alcohol plus an organic thickeningagent. After casting or extruding the powder carrying liquid upon asupporting member, the liquid is removed by a suitable absorptionerdrying procedure. As [the deliquifying proceeds the binding materialwhich forms an essential element of the slip or bath remains within thepowdered constituent and first turns into a jelly and thereafter, whenthe deliquifying has been completed, into a relatively hard igluedikesubstance which forms, with the powdered metal, a moderately strong butbrittle sheet or casting. While this may be sintered and thereafterfurther processed if care is used, we prefer to gently spray the stripor casting with a liquid of the type initially employed to form thebath, this spraying having the effect of softening and toughening thearticle and making it flexible or somewhat rubbery. When so treated itmay be handled without danger of breaking and thus may be conductedintact to a sintering furnace. In the fabrication of sheets or strips,which may be relatively wide and thin, it is highly desirable to soremoisten the article after casting and drying. Instead of weakening thedeliquified sheet or casting as might be expected, remoistening toughensthese products, thereby removing a difficulty previously encounteredwith serious consequences.

In the accompanying drawing a simple form of apparatus for carrying outthe novel process is rather diagrammatically illustrated. In thedrawing, a receptacle for the reception and retention of a bath of thecolloidal suspension of metal powder is indicated at 10, and the bath atS. The slip or slurry is formed by depositing a calculated quantity ofmetal powder in an aqueous suspension of one of the previously mentioneddispersing agents, i.e. sodium or ammonium alginate, or other alkalinealginate, or any other suitable dispersing agent having the property ofevenly distributing the suspended pulverulent material. The quantitiesof metal powder, water and dispersing agent are proportioned so that theresulting slip or slurry has a thick, heavy creamlike consistency.

A drum 13 is disposed directly above the slip containing pan or vesselfrom which the powder suspension (liquid vehicle plus suspending anddispersing agents) is directly deposited upon the surface of this drumas it rotates in the liquid suspension in the direction of arrow A at acarefully regulated speed.- The drum 13 may be formed of plaster ofParis or other suitable liquid absorbent or porous or foraminousmaterial having myriads or macroscopic openings therethrough.

The level of the upper surface of the bath S in the receptacle 10 ismaintained at a desired elevation, and the desired consistency of theslip ensured by a suitable means such as that shown, thus meansincluding a supply tank T having a delivery conduit C controlled by avalve V and a return conduit K the inlet end of which, indicated at K,is so positioned that the level of the bath is at the desired point, apump P being provided for effecting the return of suspension enteringthe return conduit to the supply tank T. The volume of suspensionentering the receptacle it) exceeds the volume removed by the action ofthe drum 13 so that a constant level of bath is maintained and thedesired gentle agitation of the suspension obtained.

Preferably means which is not illustrated but is of known type isemployed to create a vacuum within the interior of the drum for thepurpose of expediting the withdrawal of moisture from the strip R as thedrum rotates. As the moisture in strip R is removed, the dispersingagent being in suspension rather than solution, remains intermingledwith the metal particles in the strip, first asstuning a jelly-likeconsistency and then rapidly turning into a dry adhesive substance. Itthus serves as a binder and functions to consolidate the metal powderinto a coherent mass. When the strip R is completely dry it is quitebrittle and may be readily broken. To render it flexible it is gentlysprayed with liquid of the type utilized in the formation of theoriginal bath S, by means of any suitable spraying device,diagrammatically indicated at 14, causes the dry rigid strip to becomereadily flexible, having a consistency similar to that of wet tissuepaper, only stronger.

The strip R then leaves the drum 13 and passes onto a heat resistingconveyor belt 15 mounted upon rolls 16 and 17. The belt 15 supports thestrip R and causes it to move slowly through a furnace 18 where it issintered into a coherent mass. Upon leaving the sintering furnace is,the strip R is mechanically strong and of uniform but low density. Thesintc-red strip R may then be passed between pressure rolls l9 and 20where thickness reduction and densification take place. The densifiedstrip R then preferably passes onto a second heat resistant conveyorbelt 21 which is mounted on rolls 22. and 23. The conveyor belt 21 thenadvances the densified strip R through a second furnace 24- in which thedensified strip is annealed. Upon issuing from the furnace 24, the stripR is a finished metal strip of uniform density and thickness. It will beunderstood that the sintering and annealing mechanisms are ofconventional character.

Following are several specific examples by means of which a slip orslurry may be made which is suitable for practicing the presentinvention:

Example 1.To 500 cc. of distilled water add 12 /2 grams of sodiumalginate in the form of a dry granular powder. The Water and sodiumalginate are mixed with the aid of a Brookfield counter-rotating mixer,or its equivalent, for about minutes or until all of the sodium alginatehas been converted to a colloidal suspension. 3990 grams of minus 325mesh No. 316 stainless steel powder (spherical particle preferred) areslowly added and thoroughly blended into the vehicle fluid. Theresulting suspension of stainless steel powder will have a sufiicientl'yhigh viscosity to render it suitable for casting in the processdescribed heretofore.

Exam le 2.To 1200 cc. of distilled water add 6.4 grams of ammoniumalginate in the form of a dry granular powder. Gently stir the mixtureof water and ammonium alginate until all of the ammonium alginate hasbeen converted to a colloidal suspension. Slowly add 786 grams of minus200- mesh attrited beryllium powder and blend thoroughly into thevehicle fluid. When the blending is completed, the prepared slip isready for continuous casting on a porous plaster drum or its equivalentin the manner of the present invention.

Example 3.To a mixture of powders consisting of 85% stain-less steelparticles and 15% aluminum oxide particles add distilled water andsodium alginate. The proportion of water added being of the total byvolume and the proportion of sodium alginate being 2.5% of the total byweight. Again the resulting slip will have a high viscosity suitable forcasting or extruding.

As an alternative drying means or to assist in drying the strip R uponthe drum 13, a second drum 26 may be provided this being so disposedthat its surface will lightly contact the surface of the advancing stripR. The drum 26 is provided with a surface of felt or other absorbentmaterial for extraction of moisture from the strip R. The drum 26 mayalso seive as a molding drum, by providing its surface with suitableforming means. A vacuum may be established in the interior of the drumto accelerate the moisture extraction from the strip R.

It should be noted that, while in'the foregoing description referencehas been made only to alkaline alginates, as they are suitable forsuspending and dispersing stainless steel, beryllium and many othermetals and alloys in powdered form, many other suspending and dispersingagents may be similarly employed. For example, Carbopol, a B. F.Goodrich proprietary synthetic large molecule ring compound, whichthickens alcohol and other liquid by solution, may be utilized to permitpseudoplastic suspension of the metal powder. In the case of compoundsof this character, however, it has been found necessary to employ adifferent type of drying drum. In this case, the drum surface is notporous plaster of Paris, but an impervious metal surface and the vehicleis removed by evaporation. This can be accomplished by gentle heatingwhich drives oil the volatile vehicle leaving behind the metal; theparticles of which are held together by the dryin and finally driedCarbopol which acts in a manner similar to that of the alginates inproducing strong transient adhesive action. Again, similarly to thealginate which is filterable and therefore remains in the metal stripwhen it is dewatered by the porous plaster drum, these suspending mediafirst turned into a jelly-like substance and then, on subsequent drying,into strong adhesives.

While the present invention has been discussed primarily as a method ofproducing continuous webs, strips or sheets of solid metal, it will beobvious that the method is susceptible of use in the production ofproducts other than solid metal webs or strips. For example, it is alsopossible to use the method of the present invention for the productionof continuous strips or sheets of porous character and of materialssuitable for filtering purposes. The porosity of the strip can becontrolled by regulation of the amount of mechanical deformation whichtakes place during the rolling operation after the strip has beensintercd.

It is to be understood that the aforedescribed materials, apparatus andtechniques are susceptible, in utilizing the invention, considerablevariation without departure from the invention.

What is claimed is:

1. The method of producing a continuous metal strip which includes thesteps of forming a thin flowable bath comprised of metal powder and acolloidal suspension, said suspension comprising a liquid carrier and anorganic pulverulent compound which is characteristically insoluble insaid liquid carrier, separable therefrom by filtration and, when thusseparated, adapted to serve as a binder, the metal powder beingsubstantially uniformly dispersed throughout said suspension,withdrawing a portion of the bath thus formed and depositing the sameupon a support to form a strip of desired thickness, removing the liquidcontent of said strip while leaving with the metal the organic bindingcompound, consolidating the strip into a coherent mass from which theorganic material has been substantially removed by the application ofheat, and subsequently densifying the strip by a rolling operation.

2. The method set forth in claim 1 in which the deposited strip is,prior to being heated, maintained in moist condition by the applicationthereto of a quantity of said colloidal suspension.

3. The method set forth in claim 1 in which the powder introduced intothe bath comprises a mixture of powdered metal and a metal oxide.

4. The method of producing a continuous metal strip which comprises thesteps of mixing metal powder with a thickened liquid comprising asolvent and a solublc organic compound characterized by its ability tothicken the solvent and remain with the metal powder when the solvent isevaporated, said organic compound being further characterized by anability, upon evaporation of the solvent, to first assume a jelly-likeconsistency and to thereafter become a relatively hard glue-likesubstance which forms with the metal powder a moderately strong butbrittle strip, withdrawing a portion of the bath thus formed to create astrip of desired thickness, evaporating the liquid content of said stripwhile leaving with the metal the deliquefied organic compound,consolidating the strip by heat into a coherent mass from which theorganic material has been substantiall removed, and densifying the l y lct g t to a, rolling operation.

References Cited in the file of this patent UNITED STATES PATENTS2,903,787 Brennan Sept. 15, 1959 6 Wagner Mar. 15, 1960 Mouwen Apr. 11,196-1 Szymaszek Apr. -11, 1961 Thien-Chi et al. Sept. 26, 1961 MoutaudApr. 23, 196 3 FOREIGN PATENTS Great Britain Oct. 2, 1957

1. THE METHOD OF PRODUCING A CONTINUOUS METAL STRIP WHICH INCLUDES THESTEPS OF FORMING A THIN FLOWABLE BATH COMPRISED OF METAL POWDER AND ACOLLOIDAL SUSPENSION, SAID SUSPENSION COMPRISING A LIQUID CARRIER AND ANORGANIC PULVERULENT COMPOUND WHICH IS CHARACTERISTICALLY INSOLUBLE INSAID LIQUID CARRIER, SEPARABLE THEREFROM BY FILTRATION AND, WHEN THUSSEPARATED, ADAPTED TO SERVE AS A BINDER, THE METAL POWDER BEINGSUBSTANTIALLY UNIFORMLY DISPERSED THROUGHOUT SAID SUSPENSION, WITHDRAWING A PORTION OF THE BATH THUS FORMED AND DEPOSITING THE SAME UPON ASUPPORT TO FORM A STRIP OF DESIRED THICKNESS, REMOVING THE LIQUIDCONTENT OF SAID STRIP WHILE LEAVING WITH THE METAL THE ORGANIC BINDINGCOMPOUND, CONSOLIDATING THE STRIP INTO A COHERENT MASS FROM WHICH THEORGANIC MATERIAL HAS BEEN SUBSTANTILLY REMOVED BY THE APPLICATION OFHEAT, AND SUBSEQUENTLY DENSIFYING THE STRIP BY A ROLLING OPERATION. 4.THE METHOD OF PRODUCING A CONTINUOUS METAL STRIP WHICH COMPRISES THESTEPS OF MIXING METAL POWDER WITH A THICKENED LIQUID COMPRISING ASOLVENT AND A SOLUBLE ORGANIC COMPOUND CHARACTERIZED BY ITS ABILITY TOTHICKEN THE SOLVENT AND REMAIN WITH THE METAL POWDER WHEN THE SOLVENT ISEVAPORATED, SAID ORGANIC COMPOUND BEING FURTHER CHARACTERIZED BY ANABILITY, UPON EVAPORATION OF THE SOLVENT, TO FIRST ASSUME A JELLY-LIKECONSISTENCY AND TO THEREAFTER BECOME A RELATIVELY HARD GLUE-LIKESUBSTANCE WHICH FORMS WITH THE METAL POWDER A MODERATELY STRONG BUTBRITTLE STRIP, WITHDRAWING A PORTION OF THE BATH THUS FORMED TO CREATE ASTRIP OF DESIRED THICKNESS, EVAPORATING THE LIQUID CONTENT OF SAID STRIPWHILE LEAVING WITH THE METAL THE DELIQUEFIED ORGANIC COMPOUND,CONSOLIDATING THE STRIP BY HEAT INTO A COHERENT MASS FROM WHICH THEORGANIC MATERIAL HAS BEEN SUBSTANTIALLY REMOVED, AND DENSIFYING THESTRIP BY SUBJECTING IT TO A ROLLING OPERATION.